The present invention relates to a document transferring apparatus for an image forming apparatus, such as an image reading apparatus, and for example, relates to an automatic document feeder which separates a plurality of documents stacked on a document placing table into one sheet and supplies the same to an image forming apparatus, for example, an image reading apparatus.
As an automatic document feeder for an image forming apparatus, there has been generally known an apparatus disclosed in the Japanese Patent Publication (KOKAI) No. H8-133551. By referring to FIG. 9, a summary of this automatic document feeder is explained below.
In FIG. 9, numeral 1 designates an image forming apparatus main body; 2 designates a platen glass which is disposed in the image forming apparatus main body 1 for placing the document thereon in case of reading a thick document such as a book; 3 designates reading means, such as CCD, for reading the document on the platen glass 2; 4 designates an automatic document feeder attached to the image forming apparatus main body 1 to be able to open and close such that it covers the platen glass 2. Incidentally, 5 designates a platen glass for reading the document in case of automatic document feeding by using the automatic document feeder 4.
Here, the reading means 3 reads a document, which is transferred by automatic document feeding, at a predetermined reading position, and also, transfers to read the document in case the thick document such as a book is placed on the platen glass 2.
The automatic document feeder 4 is formed of a platen cover 7 including a white sheet 6 pressing a thick document, such as a book, onto the platen glass 2, a document supply table 8, an ejection table 7b formed on an upper surface of the platen cover 7, and a document transfer section 9; and is disposed to freely open and close with respect to the platen glass in the image forming apparatus.
In the document transfer section 9, documents placed on the document supply table 8 are separated into one sheet by separating means 9h disposed in a document supply part 9a, and supplied, an then a leading edge of the document abuts against register means 9i so as to align the documents. Then, the document transferred by the register means 9i to a transfer part 9c is supplied by rollers 9j and 9f, which are pressed against a feed roller 9b, to a reading position of the reading means 3 to be read. The read document is supplied by the feed roller 9b and a roller 9g to an ejection part 9e, and ejected onto the ejection table 7b by ejecting means 9k. Further, when a double-sided document is read, the document sent to the ejection part 9e is switched back, and again introduced to the transfer part 9c.
Incidentally, in the aforementioned automatic document feeder 4, when a rear edge of the document passes respectively from the separating means 9h and the register means 9i in the paper supply part 9a and from the rollers 9j and 9f disposed at an entrance of the transfer part 9c, although the feed roller 9b is rotated at the predetermined speed, the document is momentarily stopped, and it occurs that a vibration is applied to the document which is being read. Accordingly, there was a disadvantage such that quality of image (differential linearity) of the copied document after being read is deteriorated.
Furthermore, the vibration applied to the document which is being read occurs not only when the rear edge of the document is taken out from or passes through the aforementioned rollers, but also when a leading edge of the document being read abuts against a roller 9g or a guide for leading to the roller 9g located in the side of the stream lower than the reading position.
Namely, in the paper supply and ejection steps, a problem occurs whenever the rear edge of the document passes through various rollers such as the driving roller for feeding the document, or whenever the leading edge of the document abuts against the roller or the guide.
Also, in the document transfer step, especially in the paper supply steps from the paper supply part 9a to the reading position, when the printed letter or dust peeled off from the document is clung to or adhered to the platen glass 5, there is a problem such that the reading means 3 reads this printed letter and the deterioration of the image quality (black lines) occurs.
The present invention has been made in view of the aforementioned circumstances, and an object of the invention is to provide an automatic document feeder which can prevent the deterioration of the image quality in the document transfer steps.
Also, another object of the invention is to provide an automatic document feeder which can prevent the deterioration of the image quality due to the printed letters or dust peeled off from the document in the paper supply step.